CPC (Continuous Packet Connectivity), allows the user equipment (UE) to use discontinuous transmission (DTX) for DPCCH control channel in the uplink when the UE is not sending data, which saves power and increases network capacity. DPCCH bursts are control signals that enable a UE to be synchronized or connected with a network. The UE is allowed to send the DPCCH in bursts periodically to maintain synchronization or a connection with the network. When and how the UE should send the DPCCH bursts is conventionally configured by higher layers.
Experience has shown that modern networks are highly bursty. In this case, bursty transmissions may include data transmissions that are sent in short bursts, and in between the bursts are gaps when no data is sent at all. In addition, to achieve high rates in the uplink direction, it is increasingly acknowledged among network vendors that scheduling users one at a time in a Time Division (TD) scheduled manner is beneficial, since this way, only a designated user transmits control signaling or data, and there is no interference from other users, and the required high Eb/Io target can be met.
One problem with existing CPC is that, when the DPCCH burst is sent according to a pre-determined pattern, the UE has no idea whether it is going to experience a lot of interference from other UEs, or if it will experience no interference at all. If there is a lot of interference from other users during the burst, the inner loop power control in the network measures a low Signal to Interference Ratio (SIR), which will cause the UE to increase DPCCH power. When the UE transmits data again, it can transmit with too much power wasting power and causing interference in the network, especially if there is no other user interference with the data transmission. A second problem is that when the DPCCH burst is transmitted, the burst may collide with other user data transmissions, which causes interference. It may also collide with other user bursts.
CPC, as mentioned above, provides the bursts, and also DPCCH pre-ambles (prior to a user transmitting data) and DPCCH post ambles (transmitted just after a user transmits data), as illustrated in FIG. 1. A Lean Carrier solution proposes to completely remove the DPCCH bursts, and also DPCCH pre-ambles and post ambles, to remove the interference problems associated with them, as discussed above, and, in general, to reduce interference in the network. In this regard, the Lean Carrier solution aims to minimize control signaling. In the Lean carrier solution, a UE is given a grant when it needs to send data.
In some cases, it can be useful to have DPCCH bursts and DPCCH pre-ambles, and in some cases, these bursts and pre-ambles can be a problem. The bursts, particularly pre-ambles, can be useful for power control and channel tracking for a user, if the interference experienced by the bursts is similar to the interference that will be experienced when the user transmits data. However, the DPCCH bursts can be a problem if the bursts and pre-ambles/postambles are interfered with by another high rate user, and in a second case, if the bursts interfere with high rate users. CPC has no way to distinguish when a DPCCH burst will be useful or harmful. The Lean Carrier solution completely removes bursts and, therefore, cannot take advantage of when they might be useful without some modifications. In the Lean Carrier solution, the UE must always transmit data together with the DPCCH burst.